Demand response (DR) is a method in which a power supplier requests a power consumer to adjust the amount of power consumption, to adjust a balance between the supply and the demand of power. Hereafter, a demand response request being the adjustment request of the amount of power consumption will be referred to as a DR request. When receiving a DR request, the power consumer acts according to the content of this DR request. For example, if the contents of the DR request indicate the reduction of the amount of power consumption during the period from 12:00 to 14:00 tomorrow, the power consumer takes an action such as stopping an air conditioner from 12:00 to 14:00 tomorrow. As described, a period during which the adjustment of the amount of power consumption is needed will be referred to as a DR target period.
In recent years, methods of sending a DR request via the Internet (DR protocol) have been standardized. These DR protocols include, for example, Open Automated Demand Response (OpenADR). To perform a DR using the DR protocol, the power supplier prepares a system to send a DR request, and the power consumer prepares a system to receive the DR request.
Before performing a demand response, the power supplier (the sender of a DR request) and the power consumer (the receiver of the DR request) make a demand response contract (hereafter, referred to as a DR contract). Commonly, the validity or invalidity of the DR request is determined based on the sending time of the DR request, thereby the sending time is important for both the power supplier and the power consumer. If the DR request becomes invalid, the plan of electric power adjustment that the power supplier has created in advance is to be miscarried. In addition, if the DR request becomes invalid, the power consumer does not need to adjust the amount of power consumption.
Thus the validity or the invalidity of a DR request has impacts on the actions of both the power supplier and the power consumer. To achieve the adjustment of the amount of power consumption by appropriate actions of the power supplier and the power consumer, a scheme that certify the sending time of the DR request for both parties is necessary.
If a DR request could not reach the power consumer by a communication network failure, the power suppler retransmits the DR request. If the validity or the invalidity of the DR request is determined based on a sending time at which this DR request is first sent (hereafter, referred to as a first sending time), this first sending time is important for both the power supplier and the power consumer. Unfortunately, there is a problem with the retransmission of a DR request in that it is difficult to certify the first sending time.